Colored steel



May 19, 1942. c. BATCHELLER COLORED STEEL U Z N w R Egg/ O V V T w Z w 6w, M r. m 2 v M F m A 7 0 T Patented May 19, 1942 COLORED STEEL ClementsBatcheller, Glens Falls, N. Y., assignor to Allegheny Ludlum SteelCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Originalapplication June 30, 1938, Serial No.

216,719. Divided and this application February 24, 1941, Serial No.380,241

, Claims.

My invention relates to the surface coloration of stainless steels andparticularly to the production of patterns thereon of distinctive colorwhich may be purely decorative or of a utilitarian nature such as signs,badges, name plates, license plates, picture or the like.

Panels or trim of stainless steel having a uniform surface colorthroughout, either of the natural metal or as uniformly colored by myprocesses, may be very monotonous to the eye particularly when of largearea, and one of the objects of my invention therefore is to provide asimple method whereby such stainless steel surfaces may be treated toform thereon or therein decorative patterns in which the pattern and thebackground have distinctive colorations. The same method used inproducing a purely decorative effect in which the utility of thefinished article lies largely in its aesthetic characteristics may alsobe used in the production of signs, name plates, license plates, badgesand the like having, in addition to aesthetic properties, greatpractical utility because of the permanence of the article. It istherefore to be understood that the objects of my invention include theproduction of such articles.

I accomplish the foregoing and other objects by the method describedbelow and illustrated in the accompanying drawing in which- Fig. 1 is aplan view of a mask or stencil of a simple design;

Fig. 2 is a section of Fig. l in the plane 2-2;

Fig. 3 is a plan view of a surface of stainless steel decorated inaccordance with my process and in which the mask or stencil shown inFig. l is used;

Fig. 4 is a plan view of the stainless steel article shown in Fig. 3which has been treated by a modification of the process used inproducing the article of Fig. 3;

Fig. 5 is a highly magnified section of Fig. 3 in the plane 5-5;

Fig. 6 is a highly magnified section of Fig. 4 in the plane 6-6; and

Fig. 7 is a front view of a stainless steel sign or name plate producedby my process.

In carrying out my invention, I first color the surface of the steelthroughout by subjecting it to the action of an oxidizing agent for asufficient length of time to produce thereon or therein a coherent andtenaciously adherent color film. The agent employed should be of suchcharacter as to produce this film without etching or in any wayotherwise affecting the surface finish of the steel. That is to say, ifthe steel is highly polished, the oxidizing agent employed should be soadjusted that this surface is not affected in any way other than toproduce a color thereon or therein.

It i to be understood that the pattern produced on the steel may be incolor on the natural steel background or of a natural steel color on acolored background, or the pattern and the background may be bothcolored by my process but to different color or tone values.

In my copending application Serial No. 206,043 I have described a methodof coloring the surface of stainless steel by immersing the same in asolution of the following composition:

Formula. 1

Parts by weight Etching inhibitor 4-25 Sulphuric acid (1.84 sp. gr.)23-54 Water 35-64 In the above formula it will be noted that the acidconcentration in the sulphuric acid-water solution varies from 23 partsin a total of 87 parts (23+64), to 54 parts in a total of 89 parts(54-1-35), or from about 26% to about 61%.

By heating the above solution and maintaining it within a temperaturerange of about 185 F. to 200 F. a specimen of polished stainless steelof the 18-8 type (18 Cr., 8 Ni.) or a straight 17-18 chromium type whenimmersed therein for a period of about one hour will acquire a colorrunning from a light yellow gold through the bronzes and darker brownsup to a deep, jet black, depending principally upon the duration of thetreatment, the acid concentration in the solution, its temperature, andthe presence or absence of alloying elements in the steel other thanchromium.

Where a jet black color is desired, I prefer to use the ingredients inthe above formula within the following limits:

Formula 2 Parts by weight Etching inhibitor 10-14 Sulphuric acid (1.84sp. gr.) 36-50 Water 30-50 In the above formula it will be noted thatthe acid concentration in the sulphuric acid-water solution varies from36 parts in a total of 86 parts (36+50) to 50 parts in a total of parts(50+30), or from about'42% to about 63%.

The color build up is very gradual during the earlier stages of theprocessing but progresses very rapidly during the last few minutes up towhat is apparently its maximum color and film depth.

When the temperature of the solution is permitted to approach theboiling point, which is around 250 F. to 260 F., the rate of colordeposition is so extremely rapid that the film formed is neithercoherent nor adherent. Furthermore, the surface of the steel may bedestructively etched by the high acid concentration and the aestheticqualities of the product thus impaired or destroyed. Y

Where the acid concentration of the solution is materially reduced belowthat stated in Formula 2, it is difiicult, if not impossible, to producea deep black film. In this case, the color film instead of being blackmay range all the way from a dark bronze to a brass-gold color.Moreover, a much longer time is necessary in this case to produce thecolor.

While I have indicated that the temperature of the treating solution ispreferablymaintained between about 185 F. and 200 F., because this isthe best temperature to produce rapidly and economically a permanentdeep black color with my preferred formula above, a comparable resultcan be obtained by treating the steel in a solution at normal roomtemperature. In this case, however, the time necessary to produce ablack color film of equivalent thickness to that produced by mypreferred treatment requires many hours. Solutions at a temperature ofsay 70 F. are therefore workable 'but their commercial practicabilitymay be open to question because of the long time factor.

As an etching inhibitor in the above formula, I prefer to use sodiumdichromate, although other chromium salts such as ammonium dichromate,potassium dichromate or even chromium trioxide, either alone or incombination with each other or with sodium dichromate form satisfactoryinhibitors.

Where it is desired to produce a color film of less intensity, such as alight yellow gold, a bronze, or a brown film, I may use the followingsolution:

' Formula 3 I Parts by weight Etching inhibitor 4- 6 Sulphuric acid(1.84 sp. gr.) 7-11 Water 19-23 In the above formula it will be notedthat the acid concentration in the sulphuric acid-water solution variesfrom 7 parts in a total of 30 parts (7+23), to 11 parts in a total of 30parts (11+19), or from about 23% to about 37%.

The time required to form these lighter color films at the preferredtreating temperature of from 185 F. to 200 F., however, is somewhatlonger than that required to produce the black films with a higher acidconcentration. Moreover, these films are considerably less in thicknessthan the black films.

Where it is desired to produce a color more closely resembling the colorof true'gold than can be produced by theabove formulae, I use, as aninhibitor in my acid solution, a salt of the metal vanadium in place ofthe chromium. In such -a case, I prefer to use a solution of thefollowing order:

Formula 4 Parts by weight Ammonium metavanadate 4-30 Sulphuric acid(1.84 sp. gr.) 20-60 Water 35-70 (Water should be preferably free ofiron and lime.)

' monium metavanadate is employed.

solutions in about to hours where time is not an important factor.

Where the pattern to be imparted to the steel is to appear in thenatural color of the steel surface, I prepare a mask or stencil havingcut-out portions corresponding to the desired pattern.

Any suitable sheet material may be used for forming the mask or stencil,as, for example, any of the well known masking papers now on the marketin which the pattern may be cut out. One proprietary article which Ihave found very satisfactory for my purpose is sold under the trade nameScotch Tape," and is provided with an adhesive on one side whereby itmay be temporarily adhered to the surface of the steel.

In Fig. 1' of the drawing, I have shown a mask or stencil I havingcut-out portions 2 and a layer of adhesive 3 on the back thereof. Thestencil shown is adapted for use in forming a rectangular border on apanel of stainless steel colored as above described.

The stencil or mask is superimposed on the colored surface of the steelto which the pattern is to be imparted and must be held or otherwisesecured in fixed relation thereto during the buffing operationhereinafter described. Preferably, but not necessarily, it is adhesivelysecured to the colored surface of the steel. The color in those portionsof the steel which are exposed through the cut-outs in the mask is thenremoved by applying thereto a simple buifing wheel or roll carrying uponits surface a grit or rouge of such abrasive properties as will fairlyquickly and completely grind or bufi out the color and produce thedesired finish on these portions of the steel. After such bufllngoperation is completed, it is simply necessary to remove the mask tofind that the exposed portion of the colored metal is now in itsoriginal color, as shown at 4, while the colored areas which have beenprotected by the mask are completely intact, as indicated at 5 and 6.The small zones of color which remain because they were covered by theconnectors III in the mask can be buffed off after the removal of themask.

It seems obvious that the above process may be slightly modified byadhering, or otherwise holding in fixed relation, to the surface of thecolored steel, a rectangular frame-like mask such as might berepresented by the cut-outs 2 and bufling the color from the surface ofthe steel around the mask. In this case, when the mask is removed, thecolor pattern thereunder will be found intact and the background will bethe original stainless steel.

By the additional step, hereinafter described, it is possible to producea two color effect.

After removing the mask and thoroughly cleaning the surface of thesteel, it may again be immersed in any of the above solutions, for asufiicient period of time, to produce upon those portions of the surfacewhere the original color has been buffed out a color of lighter tonevalue.

For example. a bright gold tone may be imparted resulting effect is soslight as not materially to affect its original appearance.

My invention will be found extremely valuable in its adaptability toproduce very rapidly and inexpensively extremely attractive signs,tablets and the like by simply using a piece of highly polishedstainless steel colored by my process and using "stock cut-out letters,patterns and the like to produce thereon an unlimited variety ofdesigns.

The surface finish or texture of the colored portions conforms to thesurface texture or finish of the steel to which the color is applied.Hence, if it is desired to produce, for example, a dull coloredbackground or dull colored letters or patterns, the surface of thestainless steel may, before coloring, be given a slight acid pickle oreven an electro-etch to reduce its surface from the characteristic coldrolled planish to a uniformly dull surface. When a specimen so treatedis colored and the portions exposed through the mask are polished asabove described, it is possible to produce highly polished buffedletters or patterns on a dull background or dull letters or patterns ona highly polished background.

The color films produced by my process are substantially integral withthe steel and therefore do not peel, crack or craze. Microchemical testsand spectrographic analyses show the presence in the films of oxides ofthe metals in the steel, and their thickness, determined by calculationsfrom their interference colors, does not exceed about 1500 Angstromunits.

Due to the extreme thinness of the film of color, those zones where itis buffed off are not perceptibly lower than the colored zones and it isquite impossible, either by eye or by touch, to detect any diflerence inelevation of these zones. The surface of the steel seems perfectlysmooth throughout.

While I have described my invention in its preferred embodiments, it isto be understood that the words which I have used are words ofdescription rather than of limitation. Hence, changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of my invention in its broader aspects.

This application is a division of my copending application Serial No.216,719, filed June 30, P38.

What I claim is:

1. A new article of manufacture formed of stainless steel havingsubstantially integral with the surface thereof in certain zones only,an extremely thin, but coherent and tenaciously adherent film of colorcontaining oxides of iron and chromium; said colored zones being socorrelated and disposed with respect to the other zones of said surfaceas to form a predetermined design.

2. A new article of manufacture formed of stainless steel alloy havingsubstantially integral with the surface thereof in certain zones only anextremely thin film of dark color containing oxides of the metals insaid steel; said colored zones being so correlated and disposed withrespect to the other zones of said surface as to form a predetermineddesign.

3. Anew article of manufacture formed of alloy steel containing chromiumand having substantially integral with the surface thereof in certainzones only a thin lustrous film of dark color formed principally ofoxides of iron and chromium; said zones being so correlated and disposedwith respect to the other zones of said surface as to form apredetermined design.

4. A new article of manufacture formed of alloy steel containingchromium and nickel and having substantially integral with the surfacethereof in certain zones only a thin lustrous film of dark color formedprincipally of oxides of iron, nickel and chromium; said zones being socorrelated and disposed with respect to the other zones of said surfaceas to form a predetermined design.

5. A new article of manufacture formed of stainless steel alloy havingsubstantially integral with the surface thereof in certain zones only anextremely thin film of color containing. oxides of the alloying metalsin said steel; the intensity of the color in some zones differing fromthat in other zones, and said colored zones of different intensity beingso correlated and disposed with respect to each other and to theuncolored zones of said surface as to form a predetermined design.

CLEMENTS BATCHELLER;

